1. Field of the Invention
The present invention relates to a head IC which adjusts an output level of read signals of a head, a read circuit, and a media storage device, and in particular relates to a head IC which adjusts the read signals of the head with different output levels to a prescribed level, a read circuit, and a media storage device.
2. Description of the Related Art
In a media storage device, such as for example a magnetic disk device, a head reads data from media. With increases in track densities in recent years, heads have come to be supplied with a high sensitivity of detection of magnetic flux in medium, and MR (magneto-resistance) elements are used in read heads. On the other hand, as elements with still higher detection sensitivity, application of TuMR (or TMR) elements which utilize the tunneling effect is being studied.
In this way, the output levels of each read elements are not constant, and moreover the output level varies depending on changes in element characteristics due to temperature fluctuations as well as fluctuations in flying height of the head. Hence a circuit is necessary to adjust the read element output level prior to demodulation of data.
FIG. 14 shows the configuration of a media storage device of the prior art, and FIG. 15 is a block diagram of a read circuit of the prior art. As shown in FIG. 14, magnetic heads 202a and 202b which read data on media (a magnetic disk) 210 are provided at the tip of an actuator 200.
The actuator 200 rotates about a rotation axis 204, and positions the magnetic heads 202a, 202b at the desired tracks on the magnetic disk 210. The magnetic heads 202a, 202b are connected to the head IC 220 provided on the actuator 200, and the head IC 220 is connected to a control circuit 230 outside the actuator 200.
Because of the long distance from the magnetic heads 202a, 202b to the control circuit 230, there are changes in the levels of signals of the magnetic heads 202a and 202b, and noise is intermingled. In order to prevent such a level change, a head IC 220 is provided between the magnetic heads 202a, 202b and the control circuit 230, to adjust the signal level. Another object of this head IC 220 is to collect numerous signal lines between the magnetic heads and the control circuit, to facilitate wiring. For example, the control circuit 230 and head IC 220 are connected via a serial interface, and the head IC 220 and each of the magnetic heads 202a, 202b are connected by individual signal lines.
FIG. 15 shows in detail the read circuit of FIG. 14. As shown in FIG. 15, a variable-gain amplifier (preamp) 220-1 is provided in the head IC 220 connected to the read element 202-1 of the magnetic head 202a (or 202b), and the output from the read element 202 is amplified at the preset gain. The variable-gain amplifier 202-1 sets the gain for each head.
A read channel 230-1 is provided in the control circuit 230 connected to the head IC 220 and an AGC (Automatic Gain Control) amplifier 230-2 provided in the read channel 230-1 receives the output from the variable-gain amplifier 220-1 of the head IC 220.
The AGC amplifier 230-2 has a differential amplifier 230-3 and an AGC circuit 230-4. The AGC circuit 230-4 compares the output value of the differential amplifier 230-3 with a reference output value, feeds back the comparison result, adjusts the gain of the differential amplifier 230-3, and adjusts the output level of the differential amplifier 230-3 to the reference level (see for example Japanese Patent Laid-open No. 10-021647).
In this AGC circuit 230-4, high-speed feedback coefficients (frequency, gain change amount) are set so as to follow changes within one sector of a track of the magnetic disk 210, and the signal level within one sector is rendered uniform.
In the technology of the prior art, such fluctuations in output level due to fluctuations in the characteristics of the element itself or to fluctuations in the flying height or other ambient conditions have been adjusted using the AGC amplifier of the read channel.
However, due to increases in recording densities in recent years, there have been demands for TuMR elements with higher detection sensitivity than other read elements. Such high-sensitivity read elements are thought to have detection sensitivities roughly ten times that of MR elements, but scattering in the signal output level is proportionately greater. Further, because of the high detection sensitivity, fluctuations in signal level due to temperature fluctuations and fluctuations in flying height of the head are also large.
Such large fluctuations in signal level may complicate the task of adjustment using the AGC amplifier of the read channel.
Moreover, increases in recording densities have led to higher circuit frequencies, faster AGC amps for read channels are being sought, and the AGC input dynamic range is narrowing. As a result, it has become difficult to adjust for level fluctuations by modifying the AGC amplifier of the read channel.
Thus as recording densities rise, there have been limits to the ability to adjust signal levels through level adjustment by the read channel AGC when using highly sensitive read elements, and when using circuits with fast operating frequencies.